Pigments and dispersion thereof



Patented Jan. 1, 1935 Q 1,986,029

UNITED STATES: PATENT OFFICE PIGMENTS AND DISPERSION THEREOF James D. Todd Max Silverman, Chicago, 111., assignors to The Sherwin-Williams Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application November 19, 1931,

-. Serial No. 576,207 g 3 Claims. (01. 134-58) This invention relates to the treatment of pi which are preferentially wetted, the invention is ments. It has special reference to the manuapplicable to an entire line of pigments in the facture of paint andpaint pigments and ,to the manufacture of paints and other products. production of oiled pigments. It is one object of this invention to disperse 5 Pigments, as originally formed in wet processes, pigments without incurring change in the finely 5 are in finely divided form. It is essential, in divided state in which they fortuitously exist, the final form for the manufacture of paint ready as hereinbefore pointed out, when the process for application, as by the painters brush, or in is commenced. This the presentinvention acother arts, that the pigments be in finely divided complishes as actual demonstration has shown.

condition and uniformly dispersed throughout a Accordingly, this invention obviates the necessity 10 carrier or vehicle. of drying all the pigment and of grinding the In the paint industry, in the first treatment dry pigments, doing so by eliminating the step of the furnished pigments, 'for the purpose of of kiln drying and introducing a new step, or .arriving at the desired form, as in their manusteps, by means of which all or substantially all facture, the pigments are necessarily mixed with of the plastic mass from the filter press is main- 15 water wherein they are formed or held in sustained in finely divided particles while being repension. In some cases the pigments are added lieved practically en irel of its water as it is to the water. With the pigments thus uniformly being mixed with the initial oil carrier or .vehicle dispersed throughout the volume of the mixture, in a thoroughly p a l nd ell tive m n the mixture is led'to a suitable filter by means One object of the ihvention is the alteration 20 of which, so far as possible, water is removed of a wet pigment particle to create or increase therefrom. The residual plastic mass which-re-- in it a preference for a liquid vehicle other than sults from this operation ofcourse still contains water and immiscible with water.

l considerable water, and that water must be elim- Still another object of the invention is the inated,practically entirely, before the pigments incorporation ofa wet paste of pigment having 25 can be successfully incorporated with an oil carpreference for a liquid vehicle into' such a velrier or vehicle to form a paint. In the prevailing hicle with .the liberation or displacement of th practice, the plastic mass from the filter press water from the paste. is subjected to heat in a kiln, for the purpose A'particular object of the invention isthe'use of evaporating the water, the mass emerging Of a viscous -aqu us pa t f dispers d pis- 30- from the kiln in practically dry state, which is mentas a medium for dispersing the water from thereafter ground dry, and mixed dry into an oil. a Wa y past of P and for taking up This procedure, however, changes the physical the pigment-freed from its water. condition of the pigments and. they are no longer Various other and ancillary objects and adin the finely-divided state in which they origivantages of the invention will become apparent 35 nally existed and in which they are desired in from the following de p of Various exam the ultimate paint. ples of the invention which illustrate specifi- A practice i'n connection with printing inks isk, cally its use in' the paint industry. the kneading of a pulp color in a vehicle. A The new step or steps referred to may be de- 40 separation of water from the mixture occurs such scribed'as directly replacing the water of the 40 that some water may be drawn off, but all the pulp from the filter presses with pigment vehicle water is not so removed, nor is that practice, as oils, such as hydrocarbons or vegetable oils, and heretofore knownj applicable to wet pigments simultaneously dispersing the pigments therein, which are not preferentially wetted by oil. To all under such conditions and to such an extent effect removal of some of the residual portion, as to P od h grade Water-free Oiled 1 18- 45 vacuum, with or without applied heat, is somements ready for the usual thinning and use as times resorted to. a paint. This is much more simple and much This invention improves the ,manufacture of less costly than the drying and grinding in the paints,inks, and other materials containing disprevailing practices, and secures not only as good persed pigments, by successfully dispersing the a productybut indeed a better one, because of 50 wet pigments in vehicles not miscible with water, the retained original fineness of the pigment. i such as oils, fats and waxes, with the liberation The suspension of particles in liquid involves of the'water. Because the process may be used forces between the interfacialsurfaces, and these with pigments which are not preferentially wetforces in turn are depe d up Su ted by such materials, as well as-with pigments. stance at the surfaces. Certain pigments, es-' at I many he maintained in fine subdivision and be pecially those which are acid in character, such as iron blues, and chrome greens, and also any color which exists in a very finely divided state, have a much less afiinity for oil than for water, and therefore tend to agglomerate when it'is attempted to replace water in its paste by oil, as in the mixing process. In order to maintain such pigments against agglomeration, the surface character is altered so that they are easily wetted by the oil. Other pigments do not need such alteration of the surface. In both instances, the mixing of the pigments, with natural or altered surfaces, is conducted in a manner conducive to maintaining the finely divided form.

Pigments are usually of two types. One class may be a simple insoluble compound or precipitate, such as lead chromate, or a mixture of simple insoluble compounds, such as lithopone. The other class may be the lake colors or insoluble metallic salts of organic dyestuffs.

\ It is wellknown that protective colloids greatly aid the making and increase the stability 0! emulsions or suspensions. Compounds for this purpose are employed in making pigmented oils. Such compounds are by nature organosols, or materials, such as metallic soaps which are soluble in the oil vehicle. Use of the organosols places many limitations on the quality, the properties, and the pigment concentration of thick pigmented oils, so much .so that they are not wholly desirable, or are practical only in small quantities for best results.

According to the present invention we treat the acid type of pigment which is not readily wetted by oil, with a polar compound. Such a compound is one acting as if it has molecules of elongated character, with distinctive functional properties at the ends of the molecule. They act in certain instances as if the molecules orient themselves in a uniform manner, presenting a surface, or interface at which similar ends of the molecule are alined, thus giving an interface with distinctive properties on one side. We have found that lead acetate, or basic lead,acetate, appears to act as a polar compound and to function advantageously for acid pigments. The basic or lead end of the molecule is undoubtedly attracted to the pigment particle by its'acidic character, thus alining the. acetate ends of the molecules into a layer which is the presentable surface of the particle. The acetate end, being organic in structure and more like the oil, readily mixes with the oil molecules, or is wetted by them. Thus, the acidic particle, normally not wetted, or poorly wetted, by the oil is altered superficially so that it is wetted by the oil.

We' prefer. to add the polar compound to the water paste of the pigment so that the particles in their finely divided condition become superficially altered to retain the fine degree of subdivision. The lead acetate being soluble in wa-. ter may be applied by the water solution as the wet particles are being ground in the oil. Thus larger particles may be broken while in the oil, and the smaller parts become superficially altered. On being wet by the oil they are easily carried off in the oil vehicle leaving behind the water which manifests itself as a separable layer.

Other pigments which are normallywetted by the oil sufficiently to maintain their fine'subdivision under proper conditions, do not need the such cases we find that the particles of the paste freed from water in the mixing process by having a sufflciently thick suspension. We have found that the mutual rubbing of the particles on each other is effective to break the particles into finer particles and to prevent agglomeration.

In accordance with the present invention oil and a wet paste of pigment particles which are by nature or by artifice preferentially wetted by oil, as between oil and water, are added to a thick paste of oil containing pigment already wetted by .oil. The three ingredients are then kneaded or mixed, and as water separates it may be withdrawn. The use of a heavy oil-wet paste to receive a water-wet paste more effectively incorporates the'pigment particles in oil and releases them from the water. The original oilpaste is called a seed" mix'and it may be prepared in numerous ways. It maybe a portion of a batch made previously by the process of this invention. It may be a paste produced from mixing kiln-dried and ground pigments with oil, and

this may be necessary or desirable in originally beginning manufacture by this invention. Such use of kiln dried pigments will result in a final product which has a percentage of particles derived by kiln drying and a percentage of particles derived from a paste. However, after the process is started a portion of any one batch may be used to mother the instant batch. The result will then be that kiln-dried particles are practically eliminated.

Without this invention the prior art practice dictates that one merely knead and. mix the wet paste and the oil together until water separates. The oil and paste in. such a process are relatively immiscible masses. The paste is too solid for the fluidity of the oil, and the two merely slop around together in a mixer with little tendency to become incorporated together. Using the present invention, the viscous paste, practically in the form of the ultimate product, lacks the fluidity which characterizes the oil. It offers a more solid mass which is capable in the mixing process of doing work on the water-wet paste. The oil required for the additional pigment is taken up readily by the body of heavy paste. The oil may be added initially, or from time to time, as incorporation of pigment in oil is effected. The addition of oil of course dilutes or thins the heavy seed, and according to the consistency desired for the seed the oil may be withheld or added. The heavier the oil paste or seed, the more effective it is to squeeze water from the wet paste. It is also effective to produce mutual rubbing of larger particles within the mixer so that they become disintegrated into'smaller particles.

In practice we prefer to use about 100 parts of seed having a consistency comparable to that of a mixture of' 80 parts of lemon yellow and 20 parts of linseed oil. To this we may add for example, approximately 10 parts of linseed oil, and approximately 40 parts of lemon yellow pigment associated with approximately as much water in the form of a wet paste. These quantities are subject to wide variation in practice. The mixing and kneading is continued "until a separable quantity of water is released. This may be withdrawn. Then more oil and paste may be added and the process repeated. If the mixing is effected in a batch process, the batch at the end of mixing may be further'mixed with application of heat, or heat and vacuum to remove residual water, not readily removable as a liquid. If the ment.

tion agents. The following-examples illustrate.

the invention more specifically.

Example I Parts by weight Chromeyellow (in paste form) 80.0 dry content Fatty acids of linseed oil .5 Linseed oil 19.5

The fatty acid coats the particles as a polar compound either per se, or as an altered compound from a slight reaction with the lead in the pigpaste in a dough mixer. When water separates it is drawn off. The final mixing may be effected with heat and vacuum to remove. the residual water.

Example II Mix A Parts by weight Dry, ground, lemon yellow 80 Linseed oil This is well mixed in a mixer, but not to an ultimate fine division of the pigment.

Mix B Parts by weight Lemon yellow (50% water) Linseed 40 dry content 01 10 Mix B into A and mill. Water will break out of the mix, which. should be poured oif. More of Mix B may be added'and the mixing continued. The released water should be removed. This may be repeated until so little water is released, that the final water requires heat and reduced pressure to remove it.

Example III Parts by weight Chinese blue (in paste form) 30.0 dry content 0.5 dry content Linseed oil, or castor oil 69.5 dry content The above quantity, totalling 100 parts, may be added to a paste containing the same or nearly the same proportions of the same materials, and the process carried out as above described.

. In Examples Iv and III the pigment illustrates the type which is preferably altered to create or to increase a preference for wetting by oil, rather than by water. Example II illustrates a pigment The materials are ground in a thick method is directly applicable to some pigments,

while other pigments may be treated to adapt them for use in the process. The invention is not tobe considered as limited to the alteration of some pigments for such adaptation, nor to any particular method of altering such pigments, although such phases are included and are con- 4 templated as falling within the scope of the invention as defined by the appended claims.

The present invention has been described and illustrated specifically by reference to manufacture of paints, wherein it is particularly important to eliminate water. However, the invention is not to be considered as limited to this field. The pigments modified to render them highly preferentially wet by a liquid vehicle may be made and sold wet as a new product for subsequent incorporation, with or without other material, into other materials, such as hydrocarbons, fats, oils and waxes, for example, castor oil, fish oil, asphalt, the material sold under the trademark Gilsonite, natural and synthetic resin varnishes, turpentine, paraflin, etc.

The so-called wetting property herein referred to is to be understood as being a relative property determined by the aflinity of the particle and the ultimate vehicle. Some pigments may be preferentially wet by one such vehicle and not by another, or to a greater or less degree by one as compared to another.

We claim:

1. The method of incorporating'pigments in oil which comprises making a watery paste of finely divided pigments, mixing said wet paste into a viscous paste of pigment already incorporated in oil, whereby water is liberated as a separable fluid, 1

and removing said water.

2. The method of incorporating pigments in oil which comprises making a watery paste of finely divided pigments, mixing said wet paste and oil into a viscous paste of said pigment already incorporated in oil, whereby water is liberated as a separable fluid, and removing said water.

3. The method of incorporating pigments in oil 

